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      <td width="400px"><p class="toc level1"><a href="docinfo.html">Document Information</a></p>
<p class="toc level1 tocsp"><a href="gexaf.html">Preface</a></p>
<p class="toc level1 tocsp"><a href="gfirp.html">Part&nbsp;I&nbsp;Introduction</a></p>
<p class="toc level2"><a href="bnaaw.html">1.&nbsp;&nbsp;Overview</a></p>
<p class="toc level2"><a href="gfiud.html">2.&nbsp;&nbsp;Using the Tutorial Examples</a></p>
<p class="toc level1 tocsp"><a href="bnadp.html">Part&nbsp;II&nbsp;The Web Tier</a></p>
<p class="toc level2"><a href="bnadr.html">3.&nbsp;&nbsp;Getting Started with Web Applications</a></p>
<p class="toc level2"><a href="bnaph.html">4.&nbsp;&nbsp;JavaServer Faces Technology</a></p>
<p class="toc level2"><a href="giepx.html">5.&nbsp;&nbsp;Introduction to Facelets</a></p>
<p class="toc level2"><a href="gjddd.html">6.&nbsp;&nbsp;Expression Language</a></p>
<p class="toc level2"><a href="bnaqz.html">7.&nbsp;&nbsp;Using JavaServer Faces Technology in Web Pages</a></p>
<p class="toc level2"><a href="gjcut.html">8.&nbsp;&nbsp;Using Converters, Listeners, and Validators</a></p>
<p class="toc level2"><a href="bnatx.html">9.&nbsp;&nbsp;Developing with JavaServer Faces Technology</a></p>
<p class="toc level2"><a href="gkmaa.html">10.&nbsp;&nbsp;JavaServer Faces Technology Advanced Concepts</a></p>
<p class="toc level2"><a href="bnawo.html">11.&nbsp;&nbsp;Configuring JavaServer Faces Applications</a></p>
<p class="toc level2"><a href="gkiow.html">12.&nbsp;&nbsp;Using Ajax with JavaServer Faces Technology</a></p>
<p class="toc level2"><a href="gkhxa.html">13.&nbsp;&nbsp;Advanced Composite Components</a></p>
<p class="toc level2"><a href="bnavg.html">14.&nbsp;&nbsp;Creating Custom UI Components</a></p>
<p class="toc level2"><a href="bnafd.html">15.&nbsp;&nbsp;Java Servlet Technology</a></p>
<p class="toc level2"><a href="bnaxu.html">16.&nbsp;&nbsp;Internationalizing and Localizing Web Applications</a></p>
<p class="toc level1 tocsp"><a href="bnayk.html">Part&nbsp;III&nbsp;Web Services</a></p>
<p class="toc level2"><a href="gijti.html">17.&nbsp;&nbsp;Introduction to Web Services</a></p>
<p class="toc level2"><a href="bnayl.html">18.&nbsp;&nbsp;Building Web Services with JAX-WS</a></p>
<p class="toc level2"><a href="giepu.html">19.&nbsp;&nbsp;Building RESTful Web Services with JAX-RS</a></p>
<p class="toc level2"><a href="gjjxe.html">20.&nbsp;&nbsp;Advanced JAX-RS Features</a></p>
<p class="toc level2"><a href="gkojl.html">21.&nbsp;&nbsp;Running the Advanced JAX-RS Example Application</a></p>
<p class="toc level1 tocsp"><a href="bnblr.html">Part&nbsp;IV&nbsp;Enterprise Beans</a></p>
<p class="toc level2"><a href="gijsz.html">22.&nbsp;&nbsp;Enterprise Beans</a></p>
<p class="toc level2"><a href="gijre.html">23.&nbsp;&nbsp;Getting Started with Enterprise Beans</a></p>
<p class="toc level2"><a href="gijrb.html">24.&nbsp;&nbsp;Running the Enterprise Bean Examples</a></p>
<p class="toc level2"><a href="bnbpk.html">25.&nbsp;&nbsp;A Message-Driven Bean Example</a></p>
<p class="toc level2"><a href="gkcqz.html">26.&nbsp;&nbsp;Using the Embedded Enterprise Bean Container</a></p>
<p class="toc level2"><a href="gkidz.html">27.&nbsp;&nbsp;Using Asynchronous Method Invocation in Session Beans</a></p>
<p class="toc level1 tocsp"><a href="gjbnr.html">Part&nbsp;V&nbsp;Contexts and Dependency Injection for the Java EE Platform</a></p>
<p class="toc level2"><a href="giwhb.html">28.&nbsp;&nbsp;Introduction to Contexts and Dependency Injection for the Java EE Platform</a></p>
<p class="toc level2"><a href="gjbls.html">29.&nbsp;&nbsp;Running the Basic Contexts and Dependency Injection Examples</a></p>
<p class="toc level2"><a href="gjehi.html">30.&nbsp;&nbsp;Contexts and Dependency Injection for the Java EE Platform: Advanced Topics</a></p>
<p class="toc level3"><a href="gjsdf.html">Using Alternatives</a></p>
<p class="toc level4"><a href="gjsdf.html#gkhpo">Using Specialization</a></p>
<p class="toc level3 tocsp"><a href="gkgkv.html">Using Producer Methods and Fields</a></p>
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<p class="toc level3"><a href="">Using Events</a></p>
<p class="toc level4"><a href="#gkhhy">Defining Events</a></p>
<p class="toc level4"><a href="#gkhnf">Using Observer Methods to Handle Events</a></p>
<p class="toc level4"><a href="#gkhih">Firing Events</a></p>
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<p class="toc level3 tocsp"><a href="gkhjx.html">Using Interceptors</a></p>
<p class="toc level3"><a href="gkhqf.html">Using Decorators</a></p>
<p class="toc level3"><a href="gkhqc.html">Using Stereotypes</a></p>
<p class="toc level2 tocsp"><a href="gkhre.html">31.&nbsp;&nbsp;Running the Advanced Contexts and Dependency Injection Examples</a></p>
<p class="toc level1 tocsp"><a href="bnbpy.html">Part&nbsp;VI&nbsp;Persistence</a></p>
<p class="toc level2"><a href="bnbpz.html">32.&nbsp;&nbsp;Introduction to the Java Persistence API</a></p>
<p class="toc level2"><a href="gijst.html">33.&nbsp;&nbsp;Running the Persistence Examples</a></p>
<p class="toc level2"><a href="bnbtg.html">34.&nbsp;&nbsp;The Java Persistence Query Language</a></p>
<p class="toc level2"><a href="gjitv.html">35.&nbsp;&nbsp;Using the Criteria API to Create Queries</a></p>
<p class="toc level2"><a href="gkjiq.html">36.&nbsp;&nbsp;Creating and Using String-Based Criteria Queries</a></p>
<p class="toc level2"><a href="gkjjf.html">37.&nbsp;&nbsp;Controlling Concurrent Access to Entity Data with Locking</a></p>
<p class="toc level2"><a href="gkjia.html">38.&nbsp;&nbsp;Improving the Performance of Java Persistence API Applications By Setting a Second-Level Cache</a></p>
<p class="toc level1 tocsp"><a href="gijrp.html">Part&nbsp;VII&nbsp;Security</a></p>
<p class="toc level2"><a href="bnbwj.html">39.&nbsp;&nbsp;Introduction to Security in the Java EE Platform</a></p>
<p class="toc level2"><a href="bncas.html">40.&nbsp;&nbsp;Getting Started Securing Web Applications</a></p>
<p class="toc level2"><a href="bnbyk.html">41.&nbsp;&nbsp;Getting Started Securing Enterprise Applications</a></p>
<p class="toc level1 tocsp"><a href="gijue.html">Part&nbsp;VIII&nbsp;Java EE Supporting Technologies</a></p>
<p class="toc level2"><a href="gijto.html">42.&nbsp;&nbsp;Introduction to Java EE Supporting Technologies</a></p>
<p class="toc level2"><a href="bncih.html">43.&nbsp;&nbsp;Transactions</a></p>
<p class="toc level2"><a href="bncjh.html">44.&nbsp;&nbsp;Resource Connections</a></p>
<p class="toc level2"><a href="bncdq.html">45.&nbsp;&nbsp;Java Message Service Concepts</a></p>
<p class="toc level2"><a href="bncgv.html">46.&nbsp;&nbsp;Java Message Service Examples</a></p>
<p class="toc level2"><a href="gkahp.html">47.&nbsp;&nbsp;Advanced Bean Validation Concepts and Examples</a></p>
<p class="toc level2"><a href="gkeed.html">48.&nbsp;&nbsp;Using Java EE Interceptors</a></p>
<p class="toc level1 tocsp"><a href="gkgjw.html">Part&nbsp;IX&nbsp;Case Studies</a></p>
<p class="toc level2"><a href="gkaee.html">49.&nbsp;&nbsp;Duke's Tutoring Case Study Example</a></p>
<p class="toc level1 tocsp"><a href="idx-1.html">Index</a></p>
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<a name="gkhic"></a><h2>Using Events</h2>
<a name="indexterm-1570"></a><a name="indexterm-1571"></a><p>Events allow beans to communicate without any compile-time dependency. One bean can define
an event, another bean can fire the event, and yet another bean can
handle the event. The beans can be in separate packages and even in
separate tiers of the application.</p>



<a name="gkhhy"></a><h3>Defining Events</h3>
<p>An event consists of the following:</p>


<ul><li><p>The event object, a Java object</p>

</li>
<li><p>Zero or more qualifier types, the event qualifiers</p>

</li></ul>
<p>For example, in the <tt>billpayment</tt> example described in <a href="gkhpa.html">The <tt>billpayment</tt> Example: Using Events and Interceptors</a>, a <tt>PaymentEvent</tt> bean defines
an event using three properties, which have setter and getter methods:</p>

<pre>    public String paymentType;
    public BigDecimal value;
    public Date datetime;

    public PaymentEvent() {
    }</pre><p>The example also defines qualifiers that distinguish between two kinds of <tt>PaymentEvent</tt>. Every
event also has the default qualifier <tt>@Any</tt>.</p>



<a name="gkhnf"></a><h3>Using Observer Methods to Handle Events</h3>
<a name="indexterm-1572"></a><a name="indexterm-1573"></a><a name="indexterm-1574"></a><p>An event handler uses an <b>observer method</b> to consume events.</p>

<p>Each observer method takes as a parameter an event of a specific
event type that is annotated with the <tt>@Observes</tt> annotation and with any qualifiers for
that event type. The observer method is notified of an event if the
event object matches the event type and if all the qualifiers of the
event match the observer method event qualifiers.</p>

<p>The observer method can take other parameters in addition to the event parameter.
The additional parameters are injection points and can declare qualifiers.</p>

<p>The event handler for the <tt>billpayment</tt> example, <tt>PaymentHandler</tt>, defines two observer methods,
one for each type of <tt>PaymentEvent</tt>:</p>

<pre>public void creditPayment(@Observes @Credit PaymentEvent event) {
    ...
}

public void debitPayment(@Observes @Debit PaymentEvent event) {
    ...
}</pre><p>Observer methods can also be conditional or transactional:</p>


<ul><li><p>A conditional observer method is notified of an event only if an instance of the bean that defines the observer method already exists in the current context. To declare a conditional observer method, specify <tt>notifyObserver=IF_EXISTS</tt> as an argument to <tt>@Observes</tt>:</p>

<pre>@Observes(notifyObserver=IF_EXISTS)</pre><p>To obtain the default unconditional behavior, you can specify <tt>@Observes(notifyObserver=ALWAYS)</tt>.</p>

</li>
<li><p>A transactional observer method is notified of an event during the before completion or after completion phase of the transaction in which the event was fired. You can also specify that the notification is to occur only after the transaction has completed successfully or unsuccessfully. To specify a transactional observer method, use any of the following arguments to <tt>@Observes</tt>:</p>

<pre>@Observes(during=BEFORE_COMPLETION)

@Observes(during=AFTER_COMPLETION)

@Observes(during=AFTER_SUCCESS)

@Observes(during=AFTER_FAILURE)</pre><p>To obtain the default non-transactional behavior, specify <tt>@Observes(during=IN_PROGRESS)</tt>.</p>

<p>An observer method that is called before completion of a transaction may call the <tt>setRollbackOnly</tt> method on the transaction instance to force a transaction rollback.</p>

</li></ul>
<p>Observer methods may throw exceptions. If a transactional observer method throws an exception,
the exception is caught by the container. If the observer method is non-transactional,
the exception aborts processing of the event, and no other observer methods for
the event are called.</p>



<a name="gkhih"></a><h3>Firing Events</h3>
<p>To activate an event, call the <tt>javax.enterprise.event.Event.fire</tt> method. This method fires an
event and notifies any observer methods.</p>

<p>In the <tt>billpayment</tt> example, a managed bean called <tt>PaymentBean</tt> fires the appropriate
event by using information that it receives from the user interface. There are
actually four event beans, two for the event object and two for the
payload. The managed bean injects the two event beans. The <tt>pay</tt> method uses
a <tt>switch</tt> statement to choose which event to fire, using <tt>new</tt> to create
the payload.</p>

<pre>    @Inject
    @Credit
    Event&lt;PaymentEvent> creditEvent;

    @Inject
    @Debit
    Event&lt;PaymentEvent> debitEvent;

    public static final int DEBIT = 1;
    public static final int CREDIT = 2;
    private int paymentOption = DEBIT;
    ...

    @Logged
    public String pay() {
        ...
        switch (paymentOption) {
            case DEBIT:
                PaymentEvent debitPayload = new PaymentEvent();
                // populate payload ... 
                debitEvent.fire(debitPayload);
                break;
            case CREDIT:
                PaymentEvent creditPayload = new PaymentEvent();
                // populate payload ... 
                creditEvent.fire(creditPayload);
                break;
            default:
                logger.severe("Invalid payment option!");
        }
        ...
    }</pre><p>The argument to the <tt>fire</tt> method is a <tt>PaymentEvent</tt> that contains the
payload. The fired event is then consumed by the observer methods.</p>


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